Power output device with fuel cell and method therefor

ABSTRACT

An output limitation warning lamp is turned on when a possible output Qf of the fuel cell is less than a predetermined value L 2 . The output limitation warning lamp is provided at a combination meter in an instrument panel. The output limitation warning lamp is also turned on when a possible output Qb of the secondary battery is less than a predetermined value L 3 . Furthermore, the output limitation warning lamp is also turned on when an allowable drive output Qh, which is the sum of the possible output Qf of the fuel cell and the possible output Qb of the secondary battery, has been less than a required output Ed* calculated at a step before carrying out output limitation to more than a certain extent for longer than a predetermined length of time.

CROSS REFERENCE TO RELATED APPLICATION

This application is a division of and claims the benefit of priorityfrom U.S. Ser. No. 10/171,974, filed Jun. 17, 2002, and is based uponand claims the benefit of priority from the prior Japanese PatentApplication Nos. 2001-181693, filed on Jun. 15, 2001 and 2002-25507,filed on Feb. 1, 2002, the entire contents of which are incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a power output device with a fuel cell and amethod of outputting power.

2. Description of Related Art

A device, which is mounted on a vehicle and limits an actual output of afuel cell according to a required output calculated from a position ofan accelerator pedal, has been suggested (for example, Japanese PatentLaid-Open Publication No. 7-75214). The device alters operatingconditions of the fuel cell according to the required output, andperforms a control to secure that the required output is outputted fromthe fuel cell. When the possible output of the fuel cell is less thanthe required output, the device limits the actual output to the possibleoutput to prevent damage to the fuel cell.

However, with the above-mentioned art, a sense of discomfort may begiven to an operator when the device is operated. When the requiredoutput from the operator is larger than the possible output of the fuelcell, the actual output is limited to the possible output of the fuelcell. Therefore, the operator has to conclude, from experience, that therequired output is not available, whether by a failure in the poweroutput device or the fuel cell not reaching normal operating conditions.If the operator uses the same power output device periodically, he orshe can come to an appropriate conclusion. However, if the operator doesnot periodically use the power output device, it is difficult to come toan appropriate conclusion.

SUMMARY OF THE INVENTION

It is an object of the present invention to notify an operator of astate of power shortage, which is a shortage of a possible output fromenergy sources such as a fuel cell and a secondary battery.

The first aspect of the present invention is a power output device witha fuel cell as one of energy sources. The power output device includes acalculation device that calculates a parameter corresponding to apossible electric power from the fuel cell, a determining device thatcompares the calculated parameter with a predetermined value fordetermining a state of power shortage which is a shortage of thepossible electric power, and a notification device that providesnotification of the power shortage when the state of power shortage isdetermined through the determining device.

According to the power output device comprised above, the state of powershortage, which is a shortage of the possible electric power, isdetermined since the parameter corresponding to the possible electricpower from the fuel cell is compared with the predetermined value by thedetermining device, and then the state of power shortage is notified bythe notification device. Therefore, an operator can be notified that apossible output of the fuel cell is in short supply according to thepower output device.

In the power output device, the calculation device may include a cellcharacteristic determining device that determines a characteristic ofthe fuel cell and a device that calculates the parameter as a maximumoutput under a rated voltage according to the detected cellcharacteristic.

According to the above-mentioned configuration, the parameter showingthe maximum output of the fuel cell under the rated voltage can becalculated through the calculation device. Therefore, the state of powershortage which is a shortage of the possible electric power from thefuel cell can be detected from the parameter according to the poweroutput device.

In the power output device according to the first aspect of the presentinvention, the calculation device may include a cell state determiningdevice that determines a state of the fuel cell and a device thatcalculates the parameter as the amount of limiting output, which is forlimiting an output of the fuel cell, according to the determined stateof the fuel cell.

According to the above-mentioned configuration, the parameter showingthe amount of limiting output for limiting the output of the fuel cellcan be calculated through the calculation device. Therefore, the stateof power shortage which is a shortage of the possible electric powerfrom the fuel cell can be determined from the parameter.

The power output device with the amount of limiting output as theparameter may include a configuration in which the state of the fuelcell determined through the cell state determining device at leastincludes a temperature of the fuel cell.

According to the above-mentioned configuration, the amount of limitingoutput can be calculated according to the temperature of the fuel cell.

In the power output device according to the first aspect of the presentinvention, the calculation device may include a fuel pump statedetecting device that detects a state of a fuel pump for supplying fuelgas to the fuel cell and a device that calculates the parameter as theamount of limiting fuel gas which is for limiting the amount of the fuelgas supplied from the fuel pump.

According to the above-mentioned configuration, the parameter showingthe amount of limiting fuel gas which is for limiting the amount of thefuel gas supplied from the fuel pump can be calculated. Therefore, thestate of power shortage which is a shortage of the possible electricpower from the fuel cell can be determined from the parameter accordingto the power output device.

The power output device with the amount of limiting fuel gas as theparameter may include a configuration in which the state of the fuelpump detected through the fuel pump state detecting device is atemperature of a motor for the fuel pump.

According to the above-mentioned configuration, the amount of limitingfuel gas can be calculated according to the temperature of the motor forthe fuel pump.

In the power output device according to the first aspect of the presentinvention, the calculation device may include a compressor statedetecting device that detects a state of a compressor for supplyingpressurized oxidizing gas to the fuel cell and a device that calculatesthe parameter as the amount of limiting the oxidizing gas which is forlimiting the amount of oxidizing gas supplied from the compressor.

According to the above-mentioned configuration, the parameter showingthe amount of limiting oxidizing gas which is for limiting the amount ofthe oxidizing gas supplied from the compressor can be calculated.Therefore, the state of power shortage which is a shortage of thepossible electric power from the fuel cell can be detected from theparameter according to the power output device.

The power output device with the amount of limiting the oxidizing gas asthe parameter may include a configuration in which the state of thecompressor detected through the compressor state detecting device is atemperature of a motor for the compressor.

According to the above-mentioned configuration, the amount of limitingthe oxidizing gas can be calculated according to the temperature of themotor for the compressor.

In the power output device according to the first aspect of the presentinvention, the notification device may include a notification lamp forvisually carrying out the notification. According to the above-mentionedconfiguration, the operator can promptly learn the notification.

The second aspect of the present invention is a power output device witha fuel cell and a secondary battery, which can be charged with an outputfrom the fuel cell, as energy sources. The power output device includesa calculation device that calculates a parameter corresponding to apossible electric power from the secondary battery, a determining devicethat compares the calculated parameter with a predetermined value fordetermining a state of power shortage which is a shortage of thepossible electric power from the secondary battery, and a notificationdevice that provides notification of the power shortage when the stateof power shortage is determined through the determining device.

According to the power output device comprised above, the state of powershortage, which is a shortage of the possible electric power from thesecondary battery, is determined since the parameter corresponding tothe possible electric power from the secondary battery is compared withthe predetermined value by the determining device, and then the state ofpower shortage is notified by the notification device. Therefore, anoperator can be notified that a possible output of the secondary batteryis in short supply according to the power output device.

In the power output device according to the second aspect of the presentinvention, the calculation device may include a cell state detectingdevice that detects a state of the secondary battery and a device thatcalculates the parameter as the amount of limiting output, which is forlimiting an output of the secondary battery, according to the detectedstate of the secondary battery.

According to the above-mentioned configuration, the parameter showingthe amount of limiting output for limiting the output of the secondarybattery can be calculated through the calculation device. Therefore, thestate of power shortage which is a shortage of the possible electricpower from the secondary battery can be detected from the parameter.

The power output device with the amount of limiting output as theparameter may include a configuration in which the state of thesecondary battery detected through the cell state detecting device atleast includes a state of charge of the secondary battery and atemperature of the secondary battery.

According to the above-mentioned configuration, the amount of limitingthe output can be calculated according to the state of charge of thesecondary battery and the temperature of the secondary battery.

In the power output device according to the second aspect of the presentinvention, the notification device may include a notification lamp forvisually carrying out the notification. According to the above-mentionedconfiguration, the operator can promptly learn the notification.

According to the third aspect of the present invention, a power outputdevice includes a fuel cell, a secondary battery which can be chargedwith an output from the fuel cell, an inverter for driving a motor witha supplied output from the fuel cell and/or the secondary battery, arequired output calculating device that calculates a required output ofthe motor, a calculation device that calculates a parametercorresponding to the sum of a possible electric power from the fuel celland the secondary battery, a determining device that compares thecalculated parameter with a predetermined value for determining a stateof power shortage which is a shortage of the sum of the possibleelectric power from the fuel cell and the secondary battery, and anotification device that provides notification of the power shortagewhen the state of power shortage is determined through the determiningdevice.

According to the power output device comprised above, the state of powershortage, which is a shortage of the sum of the possible electric powerfrom the fuel cell and the secondary battery, is determined since theparameter corresponding to the sum of the possible electric power fromthe fuel cell and the secondary battery is compared with thepredetermined value by the determining device, and then the state ofpower shortage is notified by the notification device. Therefore, anoperator can be notified that the sum of the electric power from thefuel cell and the secondary battery is in short supply according to thepower output device.

In the power output device according to the third aspect of the presentinvention, the notification device may include a notification lamp forvisually carrying out the notification. According to the above-mentionedconfiguration, the operator can promptly learn the notification.

The fourth aspect of the present invention is a power output device witha fuel cell and a secondary battery which can be charged with an outputfrom the fuel cell as energy sources. The power output device includes afirst arithmetic device that calculates a first parameter correspondingto a possible electric power from the fuel cell, a first determiningdevice that compares the calculated first parameter with a firstpredetermined value for determining a state of power shortage which is ashortage of the possible electric power from the fuel cell, a secondarithmetic device that calculates a second parameter corresponding to apossible electric power from the secondary battery, a second determiningdevice that compares the calculated second parameter with a secondpredetermined value for determining a state of power shortage which is ashortage of the possible electric power from the secondary battery, anda notification device that provides notification of the power shortagewhen the state of power shortage is determined through either the firstor second determining device.

According to the power output device comprised above, the state of powershortage, which is a shortage of the possible electric power from thefuel cell, is determined since the first parameter corresponding to thepossible electric power from the fuel cell is compared with the firstpredetermined value by the first determining device. In addition, thestate of power shortage, which is a shortage of the possible electricpower from the secondary battery, is determined since the secondparameter corresponding to the possible electric power from thesecondary battery is compared with the second predetermined value by thesecond determining device. Then the state of power shortage is notifiedby the notification device when the state of power shortage isdetermined through either the first or second determining device.Therefore, an operator can be notified that a possible output of thefuel cell or the secondary battery is in short supply according to thepower output device.

The fifth aspect of the present invention is a power output device witha fuel cell as one of energy sources. The power output device includes afuel cell maximum output calculating device that calculates a possiblemaximum output from the fuel cell when a load is not applied on thepower output device, a device maximum output calculating device thatuses the calculated maximum output of the fuel cell for calculating apossible maximum output from the power output device, a determiningdevice that determines a state of power shortage in which the calculatedmaximum output of the power output device is less than a predeterminedvalue, and a notification device that provides notification of thedetermined power shortage.

According to the power output device of the fifth aspect of the presentinvention above, the maximum output of the fuel cell is calculated whenthe load is not applied on the power output device. An open circuitvoltage (OCV) of the fuel cell fluctuates depending on the load, and theOCV reaches the maximum when the load reaches the minimum, in otherwords, when the load is not applied. Therefore, the calculated maximumoutput of the fuel cell becomes a stable maximum value without aninfluence from the load as a factor of fluctuation. The possible maximumoutput from the power output device is calculated through the devicemaximum output calculating device with the use of the calculated maximumoutput of the fuel cell. Then the state of power shortage is determinedthrough the determining device according to the calculated maximumoutput.

If a maximum output of a fuel cell is derived from a current output ofthe fuel cell which is being operated, a state of power shortage isfrequently detected because of rapid fluctuation of the load, and thenthe power shortage is frequently notified. On the contrary, the state ofpower shortage is determined based on the stable maximum outputaccording to the power output device of the fifth aspect of the presentinvention so that the state of power shortage is notified only if anoutput of the fuel cell is lowered by a failure. Therefore, an operatorcan accurately be notified of the failure of the fuel cell without aninfluence of the load fluctuation.

In the power output device according to the fifth aspect of the presentinvention, the notification device may include a notification lamp forvisually carrying out the notification. According to the above-mentionedconfiguration, the operator can promptly learn the notification.

The sixth aspect of the present invention is a power output device witha fuel cell as one of energy sources. The power output device includes afuel cell maximum output calculating device that calculates a possiblemaximum output from the fuel cell when a load is not applied on thepower output device, a device maximum output calculating device thatuses the calculated maximum output of the fuel cell for calculating apossible maximum output from the power output device, and an indicationdevice that indicates the maximum output of the power output devicecalculated through the device maximum output calculating device when theload is applied on the power output device.

According to the power output device of the sixth aspect of the presentinvention above, the maximum output of the fuel cell is calculated whenthe load is not applied on the power output device. The calculatedmaximum output of the fuel cell, as described above, becomes a stablemaximum value without an influence from the load as a factor offluctuation. The possible maximum output from the power output device iscalculated through the device maximum output calculating device with theuse of the calculated maximum output of the fuel cell. Then thecalculated maximum output is indicated by the indication device.

If a maximum output of a fuel cell is derived from a current output ofthe fuel cell which is being operated, the maximum output frequentlyfluctuates because of rapid fluctuation of the load. On the contrary,the stable maximum output is used according to the power output deviceof the fifth aspect of the present invention so that the maximum outputof the power output device can be indicated without the influence of theload fluctuation. Therefore, an operator can accurately be notified of afailure of the fuel cell without the influence of the load fluctuation.

In the power output device according to the sixth aspect of the presentinvention, the indication device may include a meter for clearlyindicating that the maximum output of the power output device is lessthan a predetermined value. According to the above-mentionedconfiguration, the operator can reliably learn a shortage of the maximumoutput through the meter.

According to the power output device with the above-described meter, themeter may include a pointer which is movable according to the maximumoutput of the power output device, a scale board for indicating a degreeof swing of the pointer, and a caution zone provided on the scale boardfor indicating that the maximum output of the power output device isless than the predetermined value. According to the above-describedconfiguration, the operator can learn the shortage of the maximum outputby checking whether the pointer provided on the meter is pointing thecaution zone or not.

According to the above-described power output device with the pointerand the caution zone both of which are provided on the scale board ofthe meter may include a notification lamp for providing notification ofa power shortage when the pointer of the meter reaches the caution zone.According to the above-mentioned configuration, the operator canpromptly learn the notification.

In the power output device according to the sixth aspect of the presentinvention, the power output device may include a current outputcalculating device that calculates a current output from the poweroutput device and a current output indicating device that enablescomparative indication of the current output and the indication throughthe indication device. According to the above-mentioned configuration,the maximum output and the current output of the power output device canbe compared easily.

The seventh aspect of the present invention is a power output devicewith a fuel cell and a secondary battery which can be charged with anoutput from the fuel cell, for outputting power from both the cells. Thepower output device includes a fuel cell maximum output calculatingdevice that calculates a possible maximum output from the fuel cell whena load is not applied on the power output device, a device maximumoutput calculating device that calculates the sum of the calculatedmaximum output of the fuel cell and a possible maximum output from thesecondary battery as a possible maximum output from the power outputdevice, a determining device that determines a state of power shortagein which the calculated maximum output of the power output device isless than a predetermined value, and a notification device that providesnotification of the determined power shortage.

According to the power output device of the seventh aspect of thepresent invention above, the maximum output of the fuel cell iscalculated when the load is not applied on the power output device.Therefore, the calculated maximum output of the fuel cell, as describedabove, becomes a stable maximum value without an influence from the loadas a factor of fluctuation. The sum of the calculated maximum output ofthe fuel cell and the possible maximum output from the secondary batteryis calculated through the device maximum output calculating device. Thenthe state of power shortage is determined according to the calculatedmaximum output of the power output device.

If a maximum output of a fuel cell is derived from a current output ofthe fuel cell which is being operated, a state of power shortage isfrequently detected because of rapid fluctuation of the load, and thenthe power shortage is frequently notified. Especially, if a state ofcharge of a secondary battery begins to be insufficient, a state ofpower shortage is detected more frequently so that the notification ofthe power shortage is repeated more frequently according to a poweroutput device with a fuel cell and the secondary battery. On thecontrary, the state of power shortage is detected based on the stablemaximum output as described above according to the power output deviceof the seventh aspect of the present invention so that the state ofpower shortage is notified only if an output of the fuel cell is loweredby a failure. Therefore, an operator can accurately be notified of thefailure of the fuel cell without an influence of the load fluctuationeven with the power output device with the fuel cell and the secondarybattery.

The eighth aspect of the present invention is a power output device witha fuel cell and a secondary battery, which can be charged with an outputfrom the fuel cell, for outputting power from both the cells. The poweroutput device includes a fuel cell maximum output calculating devicethat calculates a possible maximum output from the fuel cell when a loadis not applied on the power output device, a device maximum outputcalculating device that calculates the sum of the calculated maximumoutput of the fuel cell and a possible maximum output from the secondarybattery as a possible maximum output from the power output device, andan indication device that indicates the maximum output calculatedthrough the device maximum output calculating device when the load isapplied on the power output device.

According to the power output device of the eighth aspect of the presentinvention above, the maximum output of the fuel cell is calculated whenthe load is not applied on the power output device. Therefore, thecalculated maximum output of the fuel cell, as described above, becomesa stable maximum value without an influence from the load as a factor offluctuation. The sum of the calculated maximum output of the fuel celland the possible maximum output from the secondary battery is calculatedthrough the device maximum output calculating device. Then thecalculated maximum output of the power output device is indicated by theindication device.

If a maximum output of a fuel cell is derived from a current output ofthe fuel cell which is being operated, the maximum output frequentlyfluctuates because of rapid fluctuation of the load. Especially, if astate of charge of a secondary battery begins to be insufficient, amaximum output of the secondary battery drops more and rapidlyfluctuates according to a power output device with a fuel cell and thesecondary battery. On the contrary, the stable maximum output is usedaccording to the power output device of the eighth aspect of the presentinvention so that the possible maximum output from the power outputdevice can be indicated without an influence of the load fluctuation.Therefore, an operator can accurately be notified of a failure of thefuel cell without the influence of the load fluctuation even with thepower output device with the fuel cell and the secondary battery.

In the power output device according to the eighth aspect of the presentinvention, the indication device may include a meter for clearlyindicating that the maximum output of the power output device is lessthan a predetermined value. According to the above-mentionedconfiguration, the operator can reliably learn a shortage of the maximumoutput through the meter.

According to the power output device with the above-described meter, themeter may include a pointer which is movable according to the maximumoutput of the power output device, a scale board for indicating a degreeof swing of the pointer, and a caution zone provided on the scale boardfor indicating that the maximum output of the power output device isless than the predetermined value. According to the above-describedconfiguration, the operator can learn the shortage of the maximum outputby checking whether the pointer provided on the meter is pointing thecaution zone or not.

The ninth aspect of the present invention is a power output device witha fuel cell as one of energy sources. The power output device includes adevice maximum output calculating device that calculates a possiblemaximum output from the power output device, a current outputcalculating device that calculates a current output from the poweroutput device, and an indication device that enables comparativeindication of the maximum output calculated through the device maximumoutput calculating device and the current output calculated through thecurrent output calculating device.

According to the power output device of the ninth aspect of the presentinvention above, the maximum output and the current output from thepower output device are comparatively indicated. Therefore, the maximumoutput and the current output of the power output device can be comparedeasily so that an operator can be notified of a power shortage from theenergy source.

In the power output device according to the ninth aspect of the presentinvention, the indication device may include a meter for clearlyindicating that the maximum output is less than a predetermined value.According to the above-mentioned configuration, the operator canreliably learn a shortage of the maximum output through the meter.

According to the power output device with the above-described meter, themeter may include a pointer which is movable according to the maximumoutput, a scale board for indicating a degree of swing of the pointer,and a caution zone provided on the scale board for indicating that themaximum output is less than the predetermined value. According to theabove-described configuration, the operator can learn the shortage ofthe maximum output by checking whether the pointer provided on the meteris pointing the caution zone or not.

According to the above-described power output device with the pointerand the caution zone may include a notification lamp for providingnotification of a power shortage when the pointer of the meter reachesthe caution zone. According to the above-mentioned configuration, theoperator can promptly learn the notification.

The tenth aspect of the present invention is a method of outputtingpower with a fuel cell as one of energy sources. The method ofoutputting power includes the steps of (a) calculating a parametercorresponding to a possible electric power from the fuel cell, (b)detecting a state of power shortage, which is a shortage of the possibleelectric power, by comparing the calculated parameter with apredetermined value, and (c) providing notification of the detectedstate of power shortage.

The method of outputting power of the tenth aspect of the presentinvention has similar effects and actions to those of the power outputdevice according to the first aspect of the present invention.Therefore, an operator can be notified that a possible output of thefuel cell is in short supply.

The eleventh aspect of the present invention is a method of outputtingpower with a fuel cell and a secondary battery, which can be chargedwith an output from the fuel cell, as energy sources. The method ofoutputting power includes the steps of (a) calculating a parametercorresponding to a possible electric power from the secondary battery,(b) detecting a state of power shortage, which is a shortage of thepossible electric power from the secondary battery, by comparing thecalculated parameter with a predetermined value, and (c) providingnotification of the detected state of power shortage.

The method of outputting power of the eleventh aspect of the presentinvention has similar effects and actions to those of the power outputdevice according to the second aspect of the present invention.Therefore, an operator can be notified that a possible output of thesecondary battery is in short supply.

The twelfth aspect of the present invention is a method of outputtingpower for controlling a power output device with a fuel cell, asecondary battery which can be charged with an output from the fuelcell, and an inverter for driving a motor with a supplied output fromthe fuel cell and/or the secondary battery. The method of outputtingpower includes the steps of (a) calculating a required output of themotor, (b) calculating a parameter corresponding to the sum of apossible electric power from the fuel cell and the secondary battery,(c) detecting a state of power shortage, which is a shortage of the sumof the possible electric power from the fuel cell and the secondarybattery, by comparing the calculated parameter with a predeterminedvalue, and (d) providing notification of the detected state of powershortage.

The method of outputting power of the twelfth aspect of the presentinvention has similar effects and actions to those of the power outputdevice according to the third aspect of the present invention.Therefore, an operator can be notified that the sum of the possibleelectric power from the fuel cell and the secondary battery is in shortsupply.

The thirteenth aspect of the present invention is a method of outputtingpower with a fuel cell and a secondary battery, which can be chargedwith an output from the fuel cell, as energy sources. The method ofoutputting power includes the steps of (a) calculating a first parametercorresponding to a possible electric power from the fuel cell, (b)detecting a state of power shortage, which is a shortage of the possibleelectric power from the fuel cell, by comparing the calculated firstparameter with a first predetermined value, (c) calculating a secondparameter corresponding to a possible electric power from the secondarybattery, (d) detecting a state of power shortage, which is a shortage ofthe possible electric power from the secondary battery, by comparing thecalculated second parameter with a second predetermined value, (e)providing notification of the state of power shortage when the state ofpower shortage is detected through either step (b) or (d).

The method of outputting power of the thirteenth aspect of the presentinvention has similar effects and actions to those of the power outputdevice according to the fourth aspect of the present invention.Therefore, an operator can be notified that a possible output from thefuel cell or the secondary battery is in short supply.

The fourteenth aspect of the present invention is a method of outputtingpower with a fuel cell as one of energy sources. The method ofoutputting power includes the steps of (a) calculating a possiblemaximum output from the fuel cell when a load is not applied on thepower output device, (b) calculating a possible maximum output from thepower output device by using the calculated maximum output of the fuelcell, (c) detecting a state of power shortage in which the calculatedmaximum output of the power output device is less than a predeterminedvalue, and (d) providing notification of the detected state of powershortage.

The method of outputting power of the fourteenth aspect of the presentinvention has similar effects and actions to those of the power outputdevice according to the fifth aspect of the present invention.Therefore, an operator can be notified of a failure of the fuel cellwithout an influence of the load fluctuation.

The fifteenth aspect of the present invention is a method of outputtingpower with a fuel cell as one of energy sources. The method ofoutputting power includes the steps of (a) calculating a possiblemaximum output from the fuel cell when a load is not applied on thepower output device, (b) calculating a possible maximum output from thepower output device by using the calculated maximum output of the fuelcell, and (c) indicating the maximum output of the power output devicecalculated through step (b) when the load is applied on the power outputdevice.

The method of outputting power of the fifteenth aspect of the presentinvention has similar effects and actions to those of the power outputdevice according to the sixth aspect of the present invention.Therefore, an operator can be notified of a failure of the fuel cellwithout an influence of the load fluctuation.

The sixteenth aspect of the present invention is a method of outputtingpower with a fuel cell and a secondary battery, which can be chargedwith an output from the fuel cell, to output power from both the cells.The method of outputting power includes the steps of (a) calculating apossible maximum output from the fuel cell when a load is not applied onthe power output device, (b) calculating the sum of the calculatedmaximum output of the fuel cell and a possible maximum output from thesecondary battery as a maximum output of the power output device, (c)detecting a state of power shortage in which the maximum outputcalculated through step (b) is less than a predetermined value, and (d)providing notification of the detected state of power shortage.

The method of outputting power of the sixteenth aspect of the presentinvention has similar effects and actions to those of the power outputdevice according to the seventh aspect of the present invention.Therefore, an operator can be notified of a failure of the fuel cellwithout an influence of the load fluctuation even with the power outputdevice with the fuel cell and the secondary battery.

The seventeenth aspect of the present invention is a method ofoutputting power with a fuel cell and a secondary battery, which can becharged with an output from the fuel cell, to output power from both thecells. The method of outputting power includes the steps of (a)calculating a possible maximum output from the fuel cell when a load isnot applied on the power output device, (b) calculating the sum of thecalculated maximum output of the fuel cell and a possible maximum outputfrom the secondary battery as a maximum output of the power outputdevice, and (c) indicating the maximum output calculated through step(b) when the load is applied on the power output device.

The method of outputting power of the seventeenth aspect of the presentinvention has similar effects and actions to those of the power outputdevice according to the eighth aspect of the present invention.Therefore, an operator can be notified of a failure of the fuel cellwithout an influence of the load fluctuation even with the power outputdevice with the fuel cell and the secondary battery.

The eighteenth aspect of the present invention is a method of outputtingpower with a fuel cell as one of energy sources. The method ofoutputting power includes the steps of (a) calculating a possiblemaximum output from a power output device, (b) calculating a currentoutput of the power output device, and (c) indicating both the maximumoutput calculated through step (a) and the current output calculatedthrough step (b) for comparison.

The method of outputting power of the eighteenth aspect of the presentinvention has similar effects and actions to those of the power outputdevice according to the ninth aspect of the present invention.Therefore, an operator can be notified of a shortage of power from theenergy source.

The present invention includes the following other aspects. According tothe first another aspect of the present invention, the predeterminedvalues compared with the parameters when each power output device oreach method of outputting power of the present invention is employed areconstant values set in advance. According to the second another aspectof the present invention, the predetermined values compared with theparameters when each power output device or each method of outputtingpower of the present invention is employed are variables fluctuatingaccording to other physical values (for example, a physical valueshowing a state of the fuel cell or a physical value showing a state ofthe secondary battery). According to the third another aspect of thepresent invention, each power output device or each method of outputtingpower of the present invention is mounted on a vehicle or adopted, andthe driver of the vehicle is notified through the notification device orstep.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and further objects, features and advantages of theinvention will become apparent from the following description ofpreferred embodiments with reference to the accompanying drawings,wherein like numerals are used to represent like elements and wherein:

FIG. 1 is a block diagram mainly showing a gas system of a power outputdevice for mounting on a vehicle as one preferred embodiment of thepresent invention;

FIG. 2 is a block diagram mainly showing an electric system of a poweroutput device for mounting on a vehicle according to this preferredembodiment;

FIG. 3 is an explanatory drawing showing an example of a combinationmeter;

FIG. 4 is an explanatory drawing schematically showing a vertical crosssection of a vehicle with the power output device;

FIG. 5 is a flow chart showing processes of electric power controlperformed by a power control unit;

FIG. 6 is a flow chart showing the first half of processes for settingthree elements performed at Step S100: electric power Ed, Eb and Ef;

FIG. 7 is a flow chart showing the latter half of processes for settingthe electric power Ed, Eb and Ef;

FIG. 8 is a graph showing a relation between a temperature Tf of a fuelcell 200 and a possible output Qf of the fuel cell;

FIG. 9 is a graph showing a relation between a SOC and a possible outputQb of the secondary battery;

FIG. 10 is a graph showing a relation between a temperature Tc around amotor of a compressor and a rate of limiting the amount of supplied airPa;

FIG. 11 is a graph showing a voltage-current characteristic map of thefuel cell;

FIG. 12 is an explanatory drawing showing an output characteristic ofthe fuel cell;

FIG. 13 is a flow chart showing a control routine controlling turning onand off an output 1 imitation warning lamp 842;

FIG. 14 is a flow chart showing a lamp-on control routine in detail;

FIG. 15 is a flow chart showing a lamp-off control routine in detail;

FIG. 16 is an explanatory drawing showing an example of a combinationmeter according to a second preferred embodiment;

FIG. 17 is a block diagram of an electric system for driving thecombination meter;

FIG. 18 is a flow chart showing a control routine of a combinationmeter;

FIG. 19 is a flow chart showing a FC maximum power XQmx calculatingroutine when idling;

FIG. 20 is an explanatory drawing showing an example of a group of mapsspecifying a voltage-current characteristic according to a temperatureof a fuel cell; and

FIG. 21 is an explanatory drawing showing a relation between an OCV anda load at a fuel cell.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following explains each preferred embodiment of the presentinvention according to a preferred embodiment applied to a vehicle andthe following items.

The First Preferred Embodiment

A. Device Configuration:

B. Electric Power Control Processes:

C. Control Processes of the Output Limitation Warning Lamp:

D. Effects:

The Second Preferred Embodiment

E. Device Configuration:

F. Meter Control Processes:

G. Effects:

The First Preferred Embodiment A. Device Configuration

FIG. 1 is a block diagram mainly showing a gas system of a power outputdevice for mounting on a vehicle as the first preferred embodiment ofthe present invention. A power output device for mounting on a vehicle100 such as a car, according to the present preferred embodiment, mainlyincludes a fuel cell 200 supplied with hydrogen gas to generate electricpower, a high-pressure hydrogen gas tank 300 for supplying hydrogen gasto the fuel cell 200, and a drive motor (described later) which outputspower through electric power generated by the fuel cell 200.

The fuel cell 200 is also supplied with oxidizing gas containing oxygensuch as air along with hydrogen gas containing hydrogen, and causeselectric-chemical reactions according to the reaction formulas shownbelow at a hydrogen electrode and an oxygen electrode to generateelectric power.

In other words, when hydrogen gas is supplied to the hydrogen electrode,and oxygen gas is supplied to the oxygen electrode, the reaction (1) iscaused on the side of the hydrogen electrode, and the reaction (2) iscaused on the side of the oxygen electrode. In the entire fuel cell, thereaction (3) is caused.H₂→2H⁺+2e ⁻  (1)2H⁺+2e ⁻+(½)O₂→H₂O  (2)H₂+(½)O₂→H₂O  (3)

The fuel cell 200 is a fuel cell stack with plural single cells stackedup. A single cell includes an electrolytic membrane (not shown), thehydrogen electrode and the oxygen electrode which are diffusionelectrodes (not shown), and two separators (not shown). In this case,the electrolytic membrane is located between the diffusion electrodesand the diffusion electrodes are located between the separators.Irregularities are formed on both sides of the separators, and theirregularities form in-single cell gas channels between the hydrogenelectrode and the oxygen electrode. Hydrogen gas supplied in theabove-described way flows in the in-single cell gas channels formedbetween one separator and the hydrogen electrode. Oxidizing gas flows inthe in-single cell gas channels formed between the other separator andthe oxygen electrode. The fuel cell stack is stored in a stack case, andis installed in a vehicle.

On the other hand, high-pressure hydrogen gas is stored in thehigh-pressure hydrogen tank 300 which discharges the high-pressurehydrogen gas at pressures ranging approximately from 20 to 35 Mpa byopening a shut valve 302 attached at the base of the tank. According tothe present preferred embodiment, four of the high-pressure hydrogen gastanks 300 are mounted in the vehicle.

In addition, the power output device for mounting on a vehicle 100 ofthe present preferred embodiment includes a hydrogen gas channel forcirculating hydrogen gas in the system, an oxidizing gas channel forcirculating oxidizing gas in the system, a water circulation channel 601for circulating water contained in oxygen off-gas, and a power controlunit 700 for controlling the entire device.

The hydrogen gas channel includes a main channel 401 originating from adischarge port of the high-pressure hydrogen gas tank 300 and ending ata supply inlet of the fuel cell 200, a circulation channel 403originating from a discharge port of the fuel cell 200 and ending at apoint midway of the main channel 401 through a pump 410, a dischargingchannel 405 for discharging impurities in circulating hydrogen gas,relief channels 407 and 409 for discharging the hydrogen gas underabnormal pressures, a leak check channel 411 for checking leakage of thehydrogen gas, and a supply channel 413 originating from a hydrogen gassupply port 428 and ending at a charge inlet of the high-pressurehydrogen gas tank 300. The present preferred embodiment uses thehigh-pressure hydrogen gas tank 300 as a supply source of hydrogen gasto discharge high-pressure hydrogen gas.

The shut valve 302 and a discharge manual valve 304 are arranged at thedischarge port of the high-pressure hydrogen gas tank 300 on the mainchannel 401. A depressurizing valve 418, a heat exchanger 420, and adepressurizing valve 422 are arranged at points midway of the mainchannel 401, and a shut valve 202 is arranged at the supply inlet of thefuel cell 200. A shut valve 204 is arranged at the discharge port of thefuel cell 200 on the circulation channel 403, and a gas-liquid separator406, pump 410, and a reverse flow preventing valve 419 are arranged atpoints midway of the circulation channel 403. A reverse flow preventingvalve 306 and a charge manual valve 308 are arranged at the charge inletof the high-pressure hydrogen gas tank 300. A shut valve 412 and ahydrogen dilutor 424 are arranged on the discharging channel 405.Furthermore, a relief valve 414, a relief valve 416, and a leak checkport 426 are arranged on the relief channel 407, the relief channel 409,and the leak check channel 411 respectively.

On the other hand, the oxidizing gas channel includes an oxidizing gassupplying channel 501 for supplying oxidizing gas to the fuel cell 200,an oxygen off-gas discharging channel 503 for discharging oxygen off-gasdischarged from the fuel cell 200, and an oxygen off-gas introducingchannel 505 for introducing oxygen off-gas to the hydrogen dilutor 424.

An air cleaner 502, a compressor 504, and a moisturizing module 506 arearranged on the oxidizing gas supplying channel 501. A pressureadjusting valve 508, the moisturizing module 506, a gas-liquid separator510, a silencer 512 and an off-gas discharging port 514 are arranged onthe oxygen off-gas discharging channel 503.

Pumps 602 and 606, a moisturizing water tank 604, and an injector 608are arranged on the water circulation 601. The pumps 410, 602 and 606,and the compressor 504 are driven by motors 410 m, 602 m, 606 m and 504m, respectively.

The power control unit 700 is comprised in the device as a microcomputerinternally including a CPU, a RAM and a ROM. The power control unit 700inputs detected results from various sensors (not shown), and controlsthe valves (202, 204, 302 and 412) and the motors (410 m, 602 m, 606 mand 504 m) for the pumps (410, 602 and 606) and the compressor 504,respectively. Control lines have been omitted to make the drawing easilyviewable. The discharge manual valve 304 and the charge manual valve 308are opened and closed manually.

First, the following explains the flow of the oxidizing gas. When thecompressor 504 is driven by the power control unit 700, air in theatmosphere as oxidizing gas is taken in, and is cleaned by the aircleaner 502. Next the air is pressurized by the compressor 504. Then thepressurized air flows through the oxidizing gas supplying channel 501,and is supplied to the fuel cell 200 through the moisturizing module506.

The supplied oxidizing gas is discharged as oxygen off-gas after beingused for the above-described electric-chemical reaction in the fuel cell200. Then the discharged oxygen off-gas flows through the oxygen off-gasdischarging channel 503, and flows back to the moisturizing module 506after flowing through the pressure adjusting valve 508.

As described above, water (H₂O) is formed according to the formula (2)on the side of the oxygen electrode of the fuel cell 200. Therefore, theoxygen off-gas discharged from the fuel 200 contains a lot of moisture.On the other hand, the oxidizing gas (air) taken in from the atmosphere,and pressurized by the compressor 504, is low-humidity gas.

According to the present preferred embodiment, the oxidizing gassupplying channel 501 and the oxygen off-gas discharging channel 503pass through the same moisturizing module. Then steam is exchangedbetween the oxidizing gas supplying channel 501 and the oxygen off-gasdischarging channel 503 to moisturize the dry oxidizing gas from thevery wet oxygen off-gas. As a result, the oxidizing gas, which flows outof the moisturizing module 506, and is supplied to the fuel cell 200,becomes wet to a certain extent. On the other hand, the oxygen off-gas,which flows out of the moisturizing module 506, and is discharged intothe atmosphere outside the vehicle, becomes dry to a certain extent.

Then the oxygen off-gas, which becomes dry to a certain extent at themoisturizing module 506 as describes above, flows into the gas-liquidseparator 510. The oxygen off-gas from the moisturizing module 506 isseparated into gas and liquid by the gas-liquid separator 510. Liquidmoisture contained in the oxygen off-gas is further removed to dry theoxygen off-gas. The removed moisture is recovered as recovered water,and is drawn by the pump 602 to be stored in the moisturizing water tank604. Then the recovered water is drawn out to the injector 608 by thepump 606, and is atomized by the injector 608 at an inlet of thecompressor 504. Then the atomized water is mixed with the oxidizing gasfrom the air cleaner 502. Therefore, the oxidizing gas flowing throughthe oxidizing gas supplying channel 501 is wetted further.

The oxygen off-gas, which becomes drier at the gas-liquid separator 510as described above, is silenced by the silencer 512. Then the oxygenoff-gas is discharged into the atmosphere outside the vehicle from theoff-gas discharging port 514.

A temperature sensor 507 is provided next to the compressor 504 on achannel connecting the compressor 504 and the moisturizing module 506.Temperatures at the motor 504 m for the compressor 504 and an inverter(not shown) connected to the motor 504 m rise since they generate heatinternally due to loss. If their temperatures rise excessively, it mayaccelerate degradation of insulators, and have an adverse effect onbearings and commutators. To prevent the above-mentioned problem, thetemperature sensor 507 detects a temperature around the motor. When thetemperature rises excessively, a control by the power control unit 700to restrain the rotational speed of the motor 504 m for the compressor504 is performed.

The following explains the flow of hydrogen gas. Under normalconditions, the discharge manual valve 304 is constantly open, and thecharge manual valve 308 is constantly closed. By the power control unit700, the shut valve 302 of the high-pressure hydrogen tank 300 and theshut valves 202 and 204 of the fuel cell 200 are open when the fuel cellsystem is driven, and they are kept closed when the fuel cell system isturned off. The shut valve 412 of the discharging channel 405 isnormally kept closed by the power control unit 700 when the fuel systemis driven. The relief valves 414 and 416 are normally kept closed unlessunder abnormal pressures.

When the device is driven and the power control unit 700 opens the shutvalve 302 as described above, hydrogen gas is discharged from thehigh-pressure hydrogen tank 300. The discharged hydrogen gas is suppliedto the fuel cell 200 after flowing through the main channel 401. Thesupplied hydrogen gas is used for the above-described electric-chemicalreactions in the fuel cell 200 and discharged as hydrogen off-gas. Thedischarged hydrogen off-gas flows back to the main channel 401 afterflowing through the circulation channel 403. Then the hydrogen off-gasis supplied back to the fuel cell 200. At this time, the hydrogenoff-gas flowing through the circulation channel 403 is given momentumand drawn into the main channel 401 by driving the pump 410 provided ata point midway of the circulation channel 403. As described above, thehydrogen gas circulates in the main channel 401 and the circulationchannel 403. On the circulation channel 403, the reverse flow preventingvalve 419 is provided between a point where the circulation channel 403is connected to the main channel 401 and the pump 410 to prevent thecirculating hydrogen off-gas from flowing reversely.

By reintroducing the hydrogen off-gas into the main channel 401 asdescribed above, apparent flow rate and flow velocity of the hydrogengas supplied to the fuel cell 200 increase, even though the amount ofhydrogen used in the fuel cell 200 is the same. Therefore, favorableconditions are provided from the point of view of supplying hydrogen tothe fuel cell 200. As a result of this, output voltage of the fuel cell200 increases.

Furthermore, impurities such as nitrogen in the air, which leaks fromthe side of the oxygen electrode to the side of the hydrogen electrodeafter permeating through the electrolytic membrane, do not collectaround the hydrogen electrode by circulating hydrogen gas. Therefore,the output voltage of the fuel cell 200 does not drop due to impuritiessuch as nitrogen.

Even if hydrogen gas is introduced uniformly in the fuel cell system,impurities constantly leak from the side of the oxygen electrode to theside of the hydrogen electrode in the fuel cell 200. Therefore, theconcentration of the impurities in the uniform hydrogen gas graduallyincreases and that of the hydrogen decreases accordingly. To obviate theabove-described problem, the shut valve 412 is provided on thedischarging channel 405 which branches from the circulation channel 403and is kept open periodically by the power control unit 700 to dischargea part of the hydrogen gas containing the impurities. A part of thehydrogen gas including the impurities is discharged from the circulationchannel by opening the shut valve 412 and pure hydrogen gas isintroduced from the high-pressure hydrogen tank 300 accordingly. As aresult of this, the concentration of the impurities in the hydrogen gasdecreases and that of the hydrogen increases. Therefore, the fuel cell200 can continuously and appropriately generate power. Though the timeinterval for opening the shut valve 412 differs depending on drivingconditions and output, it may be once in five seconds, for example.

In this connection, the output voltage of the fuel cell 200 drops onlyfor an instant and does not drop dramatically even if the shut valve 412is opened when the fuel cell generates power. No longer than one secondfor opening the shut valve 412 is preferable. For example, around 500msec is more preferable.

The hydrogen gas discharged from the shut valve 412 is supplied to thehydrogen dilutor 424 after flowing through the discharging channel 405.Oxygen off-gas is also supplied to the hydrogen dilutor 424 afterflowing through the oxygen off-gas introducing channel 505 whichbranches from the oxygen off-gas discharging channel 503. The hydrogendilutor dilutes the discharged hydrogen gas from the shut valve 412 bymixing the supplied hydrogen gas and the oxygen off-gas. The dilutedhydrogen gas is introduced into the oxygen off-gas discharging channel503 and is further mixed with the oxygen off-gas flowing in the oxygenoff-gas discharging channel 503. Then the mixed gas is exhausted intothe atmosphere outside the vehicle from the off-gas discharging port514.

The rotation speed (revolving speed) of the motor 410 m for the pump 410is controlled by the power control unit 700, and the pump 410 changesthe flow velocity of hydrogen off-gas flowing in the circulation channel403. In other words, the amount of hydrogen gas supplied as fuel iscontrolled according to the amount of consumption of electric powergenerated from the fuel cell 200. Furthermore, a temperature sensor 409is provided at the motor 410 m. Temperatures at the motor 410 m and aninverter (not shown) connected to the motor 410 m rise since theygenerate heat internally due to loss. If their temperatures riseexcessively, it may accelerate degradation of insulators and have anadverse effect on bearings and commutators. To prevent theabove-mentioned problem, the temperature sensor 409 detects atemperature around the motor. When the temperature rises excessively, acontrol by the power control unit 700 to restrain the rotational speed(revolving speed) of the motor 410 m within a predetermined value isperformed.

The two depressurizing valves, the depressurizing valve 418 for theprimary depressurization and the depressurizing valve 422 for thesecondary depressurization, are provided around an outlet of thehigh-pressure hydrogen tank 300. These two valves depressurize thehigh-pressure hydrogen gas in the high-pressure hydrogen gas tank 300 intwo steps. Specifically the depressurizing valve 418 for the primarydepressurization depressurizes the high-pressure hydrogen gas frompressures approximately ranging from 20 to 35 Mpa to pressuresapproximately ranging from 0.8 to 1 Mpa. Then the depressurizing valve422 for the secondary depressurization depressurizes the high-pressurehydrogen gas from pressures approximately ranging from 0.8 to 1 Mpa topressures approximately ranging from 0.2 to 0.3 Mpa. As a result ofthis, the fuel cell 200 is not damaged since the high-pressure hydrogengas is not supplied to the fuel cell 200.

When the depressurizing valve 418 for the primary depressurizationdepressurizes the high-pressure hydrogen gas from pressuresapproximately ranging from 20 to 35 Mpa to pressures approximatelyranging from 0.8 to 1 Mpa, discharge temperature of hydrogen dischargedfrom the high-pressure hydrogen gas tank 300 varies depending onpressure and flow rate since the discharge is accompanied by expansion.The present preferred embodiment adopts the configuration in which theheat exchanger 420 is provided between the depressurizing valve 418 forthe primary depressurization and the depressurizing valve 422 for thesecondary depressurization to exchange heat with the depressurizedhydrogen gas. The heat exchanger 420 is supplied with water coolant (notshown) which has circulated in the fuel cell 200 and the supplied watercoolant exchanges heat with the hydrogen gas whose temperature hasvaried. The hydrogen gas can be supplied to the fuel cell 200 sincetemperature of the hydrogen gas approximately changes to within anappropriate temperature range after the hydrogen gas flows through theheat exchanger 420. Therefore, electric-chemical reaction proceeds wellsince a sufficient reaction temperature can be provided so that the fuelcell 200 generates power appropriately.

As described, water (H₂O) is formed on the side of the oxygen electrodein the fuel cell 200 according to the formula (2). Then the water in thestate of steam permeates into the side of the hydrogen electrode throughthe electrolytic membrane. Therefore, the hydrogen off-gas dischargedfrom the fuel cell 200 is wet and contains a lot of moisture. Accordingto the present preferred embodiment, the gas-liquid separator 406 isprovided at a point midway of the circulation channel 403. Moisturecontained in the hydrogen off-gas is separated into gas and liquid bythe gas-liquid separator 406 and the liquid moisture is removed. Thenonly the separated gas (steam), along with other kinds of gas, isintroduced into the pump 410. As a result of this, only the gaseousmoisture is contained in the hydrogen gas so that the fuel cellcontinues generating power efficiently since moisture mixed with liquidand gas is not supplied to the fuel cell 200.

On the other hand, the pressure of the hydrogen gas supplied to the fuelcell 200 may abnormally increase and the fuel cell 200 may have aproblem if the depressurizing valve 418 or the depressurizing valve 422breaks down. To deal with the case above, the relief valve 414 isprovided on the relief channel 407 which branches after thedepressurizing valve 418 on the main channel 401, and the relief valve416 is provided at a point midway of the relief channel 409 whichbranches after the depressurizing valve 422. As a result of this, therelief valve 414 opens when pressure of the hydrogen gas in the mainchannel 401 between the depressurizing valve 418 and the depressurizingvalve 422 reaches equal to or greater than a predetermined value. Therelief valve 416 opens when pressure of the hydrogen gas in the mainchannel 401 between the depressurizing valve 422 and the fuel cell 200reaches equal to or greater than a predetermined value. Therefore, theabove-described two relief valves exhaust the hydrogen gas into theatmosphere outside the vehicle to prevent the hydrogen gas fromexceeding the predetermined value further.

When charging the high-pressure hydrogen tank 300 with hydrogen gas, ahydrogen gas supplying pipe (not shown) is connected to the hydrogen gassupplying port 428 and the charge manual valve 308 attached to thehigh-pressure hydrogen tank 300 is manually opened. As a result of this,the high-pressure hydrogen tank 300 is charged with the high-pressurehydrogen gas introduced from the hydrogen gas supplying pipe after thehigh-pressure hydrogen gas flows through the supplying channel 413. Thereverse flow preventing valve 306 is provided at the base of thehigh-pressure hydrogen tank 300 to prevent the charged hydrogen gas inthe high-pressure hydrogen tank 300 from reversely flowing.

FIG. 2 is a block diagram mainly showing an electric system of a poweroutput device for mounting on a vehicle according to this preferredembodiment. As shown in FIG. 2, the power output device for mounting ona vehicle 100 mainly includes, as an electric system, theabove-mentioned fuel cell 200, a secondary battery 800, a high-tensionconverter 810, an inverter 820, a drive motor 830, a combination meter840, and the above-mentioned power control unit 700 for controlling theentire device.

The fuel cell 200 and the inverter 820 are connected to the secondarybattery 800 in parallel through the high-tension converter 810. A diode850 for preventing current from the secondary battery 800 from passingreversely is connected in series with the fuel cell 200. Electric powergenerated from the fuel cell 200 is supplied to the secondary battery800 according to circumstances, as well as to the inverter 820. Electricpower generated from the secondary battery 800 is supplied to theinverter 820 through the high-tension converter 810. The secondarybattery is a storage cell capable of charging and discharging. Though anickel-hydrogen battery is used according to the present preferredembodiment, various types of secondary batteries can be applied.

The high-tension converter 810 increases a voltage output from thesecondary battery 800 and applies the increased voltage to the inverter820 in parallel. At this time, the high-tension converter 810 increasesthe voltage according to control signals from the power control unit700. In fact, the high-tension converter 810 includes four switchingelements (for example, a bipolar MOSFET (IGBT)) and a reactor as maincircuit elements and can increase applied DC voltage to desired DCvoltage since the switching action of these switching elements iscontrolled by the control signals from the power control unit 700. Inaddition, the high-tension converter 810 can adjust the DC voltage inputfrom the fuel cell 200 and output the adjusted voltage at the secondarybattery 800. Therefore, the secondary battery can be charged anddischarged by the functions of the high-tension converter 810.

The inverter 820 drives the drive motor 830 with electric power suppliedfrom the fuel cell 200 or the secondary battery 800. Specifically, theinverter 820 converts the DC voltage applied from the fuel cell 200 orthe secondary battery 800 into three phase AC voltage and supplies thedrive motor 830 with the three phase AC voltage. At this time, theinverter 820 adjusts amplitude (pulse amplitude, in fact) and frequencyof the three phase AC voltage which is to be supplied to the drive motor830 according to the control signals from the power control unit 700 tocontrol torque generated from the motor 830.

In fact, the inverter 820 includes six switching elements (for example,a bipolar MOSFET (IGBT)) as main circuit elements, and can convertapplied DC voltage into three phase AC voltage with desired amplitudeand frequency, since the switching action of these switching elements iscontrolled by the control signals from the power control unit 700.

The drive motor 830, for example, includes a three phase synchronousmotor and is driven by an electric power supplied through the inverter820 to generate torque at a vehicle axle (not shown).

A vehicle auxiliary machine 852 and a FC auxiliary machine 854 areconnected to a point between the secondary battery 800 and thehigh-tension converter 810. In other words, the secondary battery 800 isan electric power source for these auxiliary machines. The vehicleauxiliary machine 852 refers to various electric equipment includinglighting equipment, air-conditioning equipment and a hydraulic pump. TheFC auxiliary machine 854 refers to various electric equipment used foroperating the fuel cell 200, including the pump 410, the compressor 504,and the pumps 602 and 606.

Operation of the fuel cell 200, the high-tension converter 810 and theinverter 820 is controlled by the power control unit 700. The powercontrol unit 700 controls switching of the inverter 820, and outputsthree phase AC according to a required power at the drive motor 830. Inaddition, the power control unit 700 controls operation of the fuel cell200 and the high-tension converter 810 to provide electric poweraccording to a required power.

To carry out these controls, various sensor signals are input into thepower control unit 700. Sensors such as an accelerator pedal sensor 860,a vehicle speed sensor 862 for detecting a vehicle speed, a SOC sensor864 for detecting a state of charge of the secondary battery 800, asecondary battery temperature sensor 866 for detecting a temperature ofthe secondary battery 800, a voltage sensor 868 for detecting an outputvoltage of the fuel cell 200, an electric current sensor 870 fordetecting an output current of the fuel cell 200, and a fuel celltemperature sensor 872 for detecting a temperature of the fuel cell 200are connected to the power control unit 700. The other sensors connectedto the power control unit 700 have been omitted in FIG. 2. The SOCsensor 864 includes an electric current sensor and a voltage sensor,both of which are connected to the secondary battery 800, and the powercontrol unit 700 calculates a SOC according to an amperage of electriccurrent detected by the electric current sensor and a voltage detectedby the voltage sensor. Calculation of the SOC can be carried out inconsideration of SOC history.

The combination meter 840 is provided at an instrument panel (not shown)in a compartment of the vehicle, and has good visibility for a driver.FIG. 3 is an explanatory drawing showing an example of the combinationmeter 840. Various meters and lamps such as a fuel gauge are provided atthe combination meter 840 as shown. Element 842 is an output limitationwarning lamp for warning a driver, by turning on the lamp, that theengine is running with its output limited because of the fuel cell 200or the secondary battery operated in overload. Referring back to FIG. 2,driving of the output limitation warning lamp 842 of the combinationmeter 840 is controlled by the power control unit 700 though a driver880.

FIG. 4 is an explanatory drawing schematically showing a vertical crosssection of a vehicle with the power output device. As shown in FIG. 4,the power output device for mounting on a vehicle 100 of the presentpreferred embodiment is arranged throughout a vehicle 10. Mainly thefuel cell 200, the power control unit 700 and the compressor 504 arearranged in a front part 10 a of the vehicle 10. The hydrogen gaschannels 401 and 403 and the pump 410 are arranged in an under-floorpart 10 b. The high-pressure hydrogen tank 300 and the hydrogen gassupplying port 428 are arranged in a rear part 10 c.

The drive motor 830 for generating thrust of the vehicle 10 by generatedpower from the fuel cell 200, a gear 910 for transmitting torquegenerated from the drive motor 830 to the vehicle axle, a radiator 920for cooling the drive motor 830, a condenser 930 for an air conditioner,and a main radiator 940 for cooling the fuel cell 200 are arranged inthe front part 10 a. A sub radiator 950 for cooling the fuel cell 200 isarranged in the under-floor part 10 b. The secondary battery 800 forassisting the fuel cell 200 is arranged in the rear part 10 c.

B. Electric Power Control Processes

FIG. 5 is a flow chart showing processes of electric power controlperformed by the power control unit 700. The vehicle can be driven sincethe power control unit 700 repeatedly performs these processes alongwith the other processes to control driving of the drive motor 830.

According to the processes of electric power control, the first processis to set a driving required electric power Ed, a charge/dischargeelectric power Eb, and a FC required electric power Ef by a CPU of thepower control unit 700 (step 100). The driving required electric powerEd is an electric power which is supplied to the drive motor 830 todrive the vehicle. The charge/discharge electric power Eb is an electricpower accompanied by charging and discharging the secondary battery. TheFC required electric power Ef is an electric power required of the fuelcell 200.

FIGS. 6 and 7 are flow charts specifically showing the processes forsetting the three elements carried out at Step S100: the electric powerEd, Eb and Ef. As shown in FIG. 6, the CPU inputs an acceleratorposition AP detected by the accelerator position sensor 860 and avehicle speed V detected by the vehicle speed sensor 862 as the firstprocess of the routine (step S10). Then the CPU calculates a requiredtorque T* according to the input accelerator position AP (step S120). Anaccelerator position AP which is a degree of stepping on the acceleratoris directly related to the required torque T* required by a driver sothat the required torque T* can be calculated from the acceleratorposition AP. According to the present preferred embodiment, a relationbetween the accelerator position AP and the required torque T* is storedin a ROM of the power control unit 700 as a map in advance. Then therequired torque T* corresponding to the accelerator position AP isderived from the map to which the accelerator position AP is given.

Then the CPU performs the process of calculating a driving requiredoutput Ed* according to the calculated required torque T* and the inputvehicle V (step S130). Specifically, a driving required output Ed* iscalculated by multiplying the required torque T* by the rotation speedof the vehicle axle calculated from the vehicle speed V.

Next, the CPU performs the process of inputting a temperature Tf of thefuel cell 200 detected by the fuel cell temperature sensor 872 (step140). Then the CPU calculates a possible output Qf of the fuel cellaccording to the input temperature Tf of the fuel cell 200 (step 150).The possible output Qf of the fuel cell can be calculated according tothe temperature Tf since running state of the fuel cell 200 is reflectedin the temperature Tf. According to the present preferred embodiment, arelation between the temperature Tf of the fuel cell 200 and thepossible output Qf of the fuel cell is determined by experiment and thedetermined relation is stored in the ROM of the power control unit 700as a map in advance. Then the possible output Qf of the fuel cellcorresponding to the temperature Tf of the fuel cell 200 is derived fromthe map to which the temperature Tf of the fuel cell 200 is given. FIG.8 shows an example of a relation between the temperature Tf of a fuelcell 200 and the possible output Qf of the fuel cell. A unit of apossible output Qf is in watts.

Though the possible output Qf of the fuel cell is calculated accordingto a temperature of the fuel cell 200 at step S150, it may be calculatedaccording to a temperature of the fuel cell and other physical values(sensor output values). As other physical values, a supplied gaspressure of fuel and a temperature of water coolant can be used.

Referring back to FIG. 6, the CPU next inputs a SOC of the secondarybattery 800 detected from the SOC sensor 864 and a temperature Tb of thesecondary battery 800 detected from the secondary battery temperaturesensor 866 (step S160). Then the CPU calculates a possible output Qb ofthe secondary battery according to the input SOC and temperature Tb(step S170). According to the present preferred embodiment, relationsamong the SOC and the temperature Tb of the secondary battery 800 andthe possible output Qb of the secondary battery are determined byexperiment and the determined relations are stored in the ROM of thepower control unit 700 as a map in advance. Then the possible output Qbof the secondary battery, corresponding to the SOC and a temperature ofthe secondary battery 800, is derived from the map to which the SOC andthe temperature of the secondary battery 800 is given, since a possibleoutput of the secondary battery can be determined according to the SOCand the temperature Tb of the secondary battery 800. FIG. 9 shows anexample of a two-dimensional relation between the SOC and the possibleoutput Qb of the secondary battery when the temperature Tb is fixed. Aunit of the possible output Qb of the secondary battery is in watts.

Though the possible output Qb of the secondary battery is calculatedaccording to the SOC and a temperature of the secondary battery 800 atstep S170, it may be calculated according to both the SOC and thetemperature, and other physical values (sensor output values). As otherphysical values, a voltage, an electric current and a density ofelectrolytic solution for a lead-acid battery can be used.

Referring back to FIG. 6, the CPU next stores the sum of the possibleoutput Qf of the fuel cell calculated at step S150 and the possibleoutput Qb of the secondary battery calculated at step S170 as anallowable drive output Qh of the drive motor 830 (step S180). Then theCPU determines whether the Ed* calculated at step S130 is equal to orless than the allowable drive output Qh calculated at step S180 or not(step S190). If the CPU determines that the Ed* is equal to or less thanthe Qh, the CPU stores the Ed* as the driving required electric power Edset at the step S100 (step S200). On the other hand, if the CPUdetermines that the Ed* is higher than the Qh, the CPU stores theallowable drive output Qh as the driving required electric power Ed(step S210).

After the CPU finishes the processes at step S200 or S210, the CPUperforms the process of setting the charge/discharge electric power Ebat step S220 shown in FIG. 7. At this step, the CPU calculates thecharge/discharge electric power Eb in consideration of the allowabledrive output Qh calculated at step S180; however, the CPU restrains thecharge/discharge electric power Eb to be equal to or less than thepossible output Qb of secondary battery.

Next, the CPU inputs a temperature Tc around the motor for thecompressor 504 detected by the temperature sensor 507 (step S230). Thenthe CPU calculates a rate of limiting the amount of supplied air Paaccording to the input temperature Tc (step S240). As described above,temperatures at the motor 504 m for the compressor 504 and the inverterconnected to the motor 504 m rise since they generate heat internallydue to loss. If their temperatures rise excessively, it may acceleratedegradation of insulators and have an adverse effect on bearings andcommutators. To prevent the above-mentioned problem, the CPU restrainsthe amount of oxidizing gas supplied by the compressor 504 according tothe temperature Tc around the motor for the compressor 504 to restrainthe rotational speed of the motor 504 m.

According to the present preferred embodiment, a relation between thetemperature Tc and a rate of limiting the amount of supplied air Pa isdetermined by experiment and the determined relation is stored in theROM of the power control unit 700 as a map in advance. Then a rate oflimiting the amount of supplied air Pa corresponding to the temperatureTc around the motor is derived from the map to which the temperature Tcaround the motor is given. FIG. 10 shows an example of a relationbetween the temperature Tc around the motor for the compressor 504 and arate of limiting the amount of supplied air Pa. As shown, when thetemperature Tc around the motor for the compressor 504 exceeds apredetermined value Ti (>100° C.), a rate of limiting the amount ofsupplied air Pa gradually drops as the temperature Tc rises. The unitsof a rate of limiting the amount of supplied air Pa are percentages.

Referring back to FIG. 7, the CPU inputs a temperature Tp around themotor for the pump 410 (a hydrogen pump hereafter) detected by thetemperature sensor 409 (step S250) after performing step S240. Then theCPU calculates a rate of limiting the rotational speed of the hydrogenpump Pf according to the input temperature Tp (step S260). As describedabove, temperatures at the motor 410 m for the hydrogen pump 410 and theinverter connected to the motor 410 m rise since they generate heatinternally due to loss. If their temperatures rise excessively, it mayaccelerate degradation of insulators and have an adverse effect onbearings and commutators. To prevent the above-mentioned problem, theCPU restrains the rotational speed of the motor 410 m for the hydrogenpump 410 according to the temperature Tp around the motor for thehydrogen pump 410.

According to the present preferred embodiment, a relation between thetemperature Tp and a rate of limiting the rotational speed of thehydrogen pump Pf is determined by experiment and the determined relationis stored in the ROM of the power control unit 700 as a map in advance.Then a rate of limiting the rotational speed of the hydrogen pump Pfcorresponding to the temperature Tp is derived from the map to which thetemperature Tp is given. Like the map for calculating a rate of limitingthe amount of supplied air Pa shown in FIG. 10, a rate of limiting therotational speed of the hydrogen pump Pf gradually drops as thetemperature Tc rises when the temperature Tp exceeds a predeterminedvalue (>100° C.). The units of the rate of limiting the rotational speedof the hydrogen pump Pf is in percentages. Though a rate of limiting therotational speed of the hydrogen pump Pf is used as a parametercorresponding to the temperature Tp according to the present preferredembodiment, the amount of hydrogen supplied, which is equivalent to arate of limiting the rotational speed of the hydrogen pump Pf, mayinstead be used as a parameter.

Referring back to FIG. 7, the CPU restrains the rotational speed of thehydrogen pump 410 to assure that the rotational speed does not exceedthe rate of limiting the rotational speed of the hydrogen pump Pfcalculated at step S260, as well as restraining supply of oxidizing gasto assure that the supply does not exceed the rate of limiting theamount of supplied air Pa calculated at step S240 (step S265) afterperforming step S260. The CPU next inputs an output voltage V and anoutput electric current I detected by the voltage sensor 868 and theelectric current sensor 870 respectively (step S270). Then the CPUcalculates a FC maximum power Qmx according to the input output voltageV and output electric current I (step S280). The FC maximum power Qmx isa parameter indicating a maximum output of the fuel cell 200 under asufficient voltage (a rated voltage, for example, 240V).

FIG. 11 shows a voltage-current characteristic map of the fuel cell 200.An Af1 curve shows that the fuel cell is under normal conditions and anAf2 curve shows that the fuel cell's performance has dropped because thefuel cell has been left unattended for a long period. If the fuel cell'sperformance has dropped, a point where a voltage begins to drop shiftsto the side of a lower electric current as shown in the graph. When avoltage is the rated voltage (V₀, for example, 240V), the electriccurrent is extremely low so that a required electric current cannot beoutput. To obviate the problem above, the power control unit 700calculates a voltage-current characteristic map of the fuel cell 200from the output voltage V and the output electric current I detected bythe voltage sensor 868 and the electric current sensor 870,respectively. Next, the power control unit 700 calculates an outputelectric current (I₀) according to the voltage-current characteristicmap. Then the power control unit 700 calculates the FC maximum power Qmxfrom the product of V₀ and I₀ and specifies that the calculated FCmaximum power Qmx is an upper limit of a possible output of the fuelcell 200.

When supplies of fuel gas and oxidizing gas are not sufficient, theoutput voltage V₀ cannot be obtained even from a maximum electriccurrent determined by both the supplies. In this case, the FC maximumpower Qmx is set to be an output under an output voltage determined fromthe maximum electric current. In other words and specifically, the FCmaximum power Qmx is calculated according to supplies of the fuel gasand the oxidizing gas in addition to an output voltage V and an outputelectric current I of the fuel cell.

Referring back to FIG. 7, the CPU performs the process of setting the FCrequired electric power Ef, which is a required electric power from thefuel cell 200 (step S290), after performing step S280. The FC requiredelectric power Ef is calculated from the sum of the three elements: thedriving required electric power Ed set at step S200 or S210, thecharge/discharge electric power Eb set at step 220, and an auxiliarymachine electric power Es. An auxiliary machine electric power Es is arequired electric power to drive the vehicle auxiliary machine 852 andthe FC auxiliary machine 854. If the value calculated from the sum ofthe three elements exceeds either the possible output of the fuel cellQf calculated at step S150 or the FC maximum power Qmx calculated atstep S280, the value is set to be the FC required electric power Ef atstep S290.

After carrying out step S290, the processes of the routine for settingEd, Eb, and Ef are ended by proceeding to “return”. According to theroutine, four parameters corresponding to a possible electric power fromthe fuel cell 200, which are the possible output Qf of the fuel cell,the FC maximum power Qmx, a rate of limiting the amount of supplied airPa and a rate of limiting the rotational speed of the hydrogen pump Pf,are used to restrain the FC required electric power Ef so that an outputfrom the fuel cell 200 is restrained.

In addition, the possible output Qb of the secondary battery as aparameter corresponding to a possible electric power from the secondarybattery 800 is used to restrain the charge/discharge electric power Ebso that an output from the secondary battery 800 is restrained.Furthermore, the allowable drive output Qh as a parameter correspondingto the sum of a possible electric power from the fuel cell 200 and thesecondary battery 800 is used to restrain the driving required electricpower Ed so that an output from the drive motor 830 is restrained.

When the processes of the routine for setting Ed, Eb, and Ef (step S100in FIG. 5) are ended, the CPU proceeds to the next routine (step S300).At this step, the CPU sets an output voltage of the fuel cell 200 tosecure that the FC required electric power Ef set at step S100 is outputand restrains a flow rate of gas in the fuel cell 200. A voltage is setfrom the following maps. FIG. 12 is an explanatory drawing showing anoutput characteristic of the fuel cell 200. The upper graph shows arelation between an electric power and an electric current and the lowergraph shows a relation between a voltage and an electric power.

An output characteristic of the fuel cell 200 fluctuates according to aflow rate of the supplied gas. In the lower graph, an Af3 curve showsthat the flow rate of the gas is low and an Af4 curve shows that theflow rate of the gas is high. If the rate is low, a point where thevoltage begins to drop shifts to the side of a low electric current.

An electric current Ifc corresponding to the FC required electric powerEf can be calculated according to an electric power-electric currentcharacteristic map shown in the upper graph. A voltage Vfc correspondingto the electric current Ifc can be calculated according to avoltage-electric current characteristic map shown in the lower graph. Ifthe flow rate of the gas in the fuel cell 200 is low and a requiredelectric power with a sufficient voltage cannot be output, a targetvalue of the flow rate of the gas is set according to thesecharacteristic maps.

Referring back to FIG. 5, the power control unit 700 then controls anoutput voltage of the high-tension converter 810 to obtain the outputvoltage of the fuel cell 200 set at step S300 and the charge/dischargeelectric power Eb set at step S100, as well as controlling the inverter820 to assure that a required electric power is supplied to the drivemotor 830 (step S400). An electric power according to the flow rate ofthe gas is output from the fuel cell 200 accompanied by switching of theinverter 820. An electric power according to a difference between anelectric power output from the fuel cell 200 and an electric powerconsumed at the inverter 820 is charged into or discharged from thesecondary battery 800. When the output from the fuel cell 200 respondsmore slowly than expected, electric power, which is a difference betweenthe FC required electric power Ef and the actual electric power, issupplemented by the secondary battery 800. The electric power from thesecondary battery 800 gradually drops as the output from the fuel cell200 reaches closer to the FC required electric power Ef. With theabove-described controls, electric power can be supplied with highresponsiveness.

The electric power from at least the secondary battery is assuredlysupplied to the vehicle auxiliary machine 852 and the FC auxiliarymachine 854. When the secondary battery is charged, electric powereither from the fuel cell 200 or the drive motor 830 may be supplied tothese auxiliary machines.

C. Control Processes of the Output Limitation Warning Lamp

FIG. 13 is a flow chart showing a control routine controlling turning onand off an output limitation warning lamp 842. This control routine isrepeatedly performed after every predetermined period. As shown in theflow chart, the CPU of the power control unit 700 determines whether theoutput limitation warning lamp 842 is currently on or not at the firstprocess of the routine (step S600). If the CPU determines that the lampis not on (off), the CPU carries out a lamp-on control routine forturning on the output limitation warning lamp 842 (step S700). On theother hand, if the CPU determines that the lamp is on, the CPU carriesout a lamp-off control routine for turning off the output limitationwarning lamp 842 (step S800). After carrying out step S700 or step S800,the CPU ends this control routine for the moment by proceeding to“return.”

FIG. 14 is a flow chart showing a lamp-on control routine in detail.When this routine begins, the CPU determines if the following conditionsfrom the first condition to the sixth one are met.

The first on-condition; the CPU determines whether the FC maximum powerQmx, which is one of the parameters calculated in the electric powercontrol processing routine, is less than a predetermined value L1 (stepS710).

The second on-condition; the CPU determines whether the possible outputQf of the fuel cell, which is one of the above-mentioned parameters, isless than a predetermined value L2 (step S720).

The third on-condition; the CPU determines whether the possible outputQb of the secondary battery, which is one of the above-mentionedparameters, is less than a predetermined value L3 (step S730).

The fourth on-condition; the CPU determines whether the rate of limitingthe amount of supplied air Pa, which is one of the above-mentionedparameters, is less than a predetermined value L4 (step S740).

The fifth on-condition; the CPU determines whether the rate of limitingthe rotational speed of the hydrogen pump Pf, which is one of theabove-mentioned parameters, is less than a predetermined value L5 (stepS750).

The sixth on-condition; the CPU determines whether the allowable driveoutput Qh, which is one of the above-mentioned parameters and the sum ofthe possible output Qf of the fuel cell and the possible output Qb ofthe secondary battery, is less than a value calculated by multiplyingthe required output Ed* calculated at step S130, which is a step beforecarrying out the output limitation, by a predetermined value L6 (stepS760). Then the CPU determines whether the determination result of stepS760 has been continuously affirmative for more than one second (stepS770, S780, and step S790). The above-mentioned predetermined values L1through L6 are constant values stored in the ROM of the power controlunit 700 in advance.

If any of the above-mentioned on-conditions is met, the CPU proceeds tostep S792 and turns on the output limitation warning lamp 842. Then theCPU proceeds to “return.” On the other hand, if none of theabove-mentioned on-conditions is met, the CPU proceeds to “return.”

FIG. 15 is a flow chart showing a lamp-off control routine in detail.When this routine begins, the CPU determines if the following conditionsfrom the first condition to the sixth one are met.

The first off-condition; the CPU determines whether the FC maximum powerQmx, which is one of the parameters calculated in the electric powercontrol routine, is equal to or more than a predetermined value K1 (stepS810).

The second off-condition; the CPU determines whether the possible outputQf of the fuel cell, which is one of the above-mentioned parameters, isequal to or more than a predetermined value K2 (step S820).

The third off-condition; the CPU determines whether the possible outputQb of the secondary battery, which is one of the above-mentionedparameters, is equal to or more than a predetermined value K3 (stepS830).

The fourth off-condition; the CPU determines whether the rate oflimiting the amount of supplied air Pa, which is one of theabove-mentioned parameters, is equal to or more than a predeterminedvalue K4 (step S840).

The fifth off-condition; the CPU determines whether the rate of limitingthe rotational speed of the hydrogen pump Pf, which is one of theabove-mentioned parameters, is equal to or more than a predeterminedvalue K5 (step S850).

The sixth off-condition; the CPU determines whether the allowable driveoutput Qh, which is one of the above-mentioned parameters and the sum ofthe possible output Qf of the fuel cell and the possible output Qb ofthe secondary battery, is equal to or more than a value calculated bymultiplying the required output Ed* calculated at step S130, which is astep performed before carrying out the output limitation, by apredetermined value K6 (step S860). The above-mentioned predeterminedvalues K1 through K6 are constant values stored in the ROM of the powercontrol unit 700 in advance.

If all of the above-mentioned off-conditions are met, the CPU proceedsto step S870 and turns off the output limitation warning lamp 842. Thenthe CPU proceeds to “return.” On the other hand, if any of theabove-mentioned off-conditions is not met, the CPU proceeds to “return.”The predetermined values K1 through K6 in the lamp-off control routinefor comparing the off-conditions are smaller than the predeterminedvalues L1 through L6 in the lamp-on control routine for comparing theon-conditions, respectively, due to providing hysteresis between the oncontrol and the off control.

D. Effects

According to the preferred embodiment as comprised above, the outputlimitation warning lamp 842 is turned on when the possible output Qf ofthe fuel cell is less than the predetermined value L2. According to thepreferred embodiment, a driver can immediately be notified that thepossible output of the fuel cell 200 has been reduced, through turningon the output limitation warning lamp 842 since the output limitationwarning lamp 842 is provided at the combination meter 840 in theinstrument panel.

The output limitation warning lamp 842 is also turned on when the FCmaximum power Qmx is less than the predetermined value L2. Even when thepossible output of the fuel cell 200 is reduced because of limitation ofthe FC maximum power Qmx, the driver can be notified of the shortagesince the output limitation warning lamp 842 is also turned on.Furthermore, the output limitation warning lamp 842 is turned on whenthe rate of limiting the amount of supplied air Pa is less than thepredetermined value L4 or the rate of limiting the rotational speed ofthe hydrogen pump Pf is less than predetermined value L5. Even when theair supply is limited by the rate of limiting the amount of supplied airPa and the rotational speed of the hydrogen pump is limited by the rateof limiting the rotational speed of the hydrogen pump Pf so that apossible output of the fuel cell 200 is limited and in short supply, thedriver can immediately be notified of the shortage through turning onthe output limitation warning lamp 842.

In addition, the output limitation warning lamp 842 is also turned onwhen the possible output Qb of the secondary battery is less than thepredetermined value L3 according to the preferred embodiment. Even whena possible output of the secondary battery 800 is limited in thepossible output Qb of the secondary battery and in short supply, thedriver can immediately be notified of the shortage through turning onthe output limitation warning lamp 842.

Furthermore, the output limitation warning lamp 842 is also turned onwhen the allowable drive output Qh, which is the sum of the possibleoutput Qf of the fuel cell and the possible output Qb of the secondarybattery, is less than the required output Ed* calculated at step S130,which is a step before carrying out the output limitation, to more thana certain extent. Even when the sum of an electric power from the fuelcell 200 and the secondary battery 800 is in short supply, the drivercan immediately be notified of the shortage through the turning on ofthe output limitation warning lamp 842.

According to the preferred embodiment, turning on the output limitationwarning lamp 842 is carried out through two configurations. One is basedon each parameter corresponding to a possible electric power from thefuel cell 200, which are the possible output Qf of the fuel cell, the FCmaximum power Qmx, the rate of limiting the amount of supplied air Pa,and the rate of limiting the rotational speed of the hydrogen pump Pf.The other is based on a parameter corresponding to a possible electricpower from the secondary battery 800, which is the possible output Qb ofthe secondary battery. Therefore, the driver can be notified of anoutput shortage more accurately.

Though this configuration, in which the output limitation warning lamp842 is turned on, is adopted as a notification means to notify a driverof a power shortage according to the preferred embodiment, aconfiguration in which a warning buzzer is rung may instead be adopted.In addition, the driver may be notified of the power shortage through asense of touch by vibration. Furthermore, a configuration in which eachparameter is indicated on a display, in addition to turning on theoutput limitation warning lamp 842, may be adopted. It is preferablethat normal values be indicated when the configuration in which eachparameter is indicated is adopted.

Though the predetermined values L1 through L6 in the lamp-on controlroutine for comparing the on-conditions are constant values, they may beother physical values, for example they may be variables fluctuatingaccording to a state of the fuel cell or that of the secondary battery.Regarding the predetermined values K1 through K6 in the lamp-off controlroutine for comparing the off-conditions, they may also be similarvariables.

The Second Preferred Embodiment E. Device Configuration

The following explains the second preferred embodiment. Compared withthe first preferred embodiment, a power output device for mounting on avehicle according to the second preferred embodiment includes much thesame hardware configuration. The same parts are numbered the same as inthe first preferred embodiment. A gas system of the second preferredembodiment is exactly the same with the one of the first preferredembodiment. Regarding the electric system, only the configuration of thecombination meter is different from that of the combination meter of thefirst preferred embodiment, and the other configurations are the same.

FIG. 16 is an explanatory drawing showing an example of a combinationmeter 1010 according to the second preferred embodiment. As shown, acombination meter 1010 includes the same configuration as that of thefirst preferred embodiment except for a power meter 1020 added to theconfiguration. The power meter 1020 is a meter showing a possiblemaximum electric power PWmx from the power output device for mounting ona vehicle and an electric power PW currently output from the poweroutput device for mounting on a vehicle. The power meter 1020 is ananalog meter including two pointers: a long hand 1022 and a short hand1024. The long hand 1022 shows the maximum electric power PWmx and theshort hand shows the electric power PW currently output.

A scale board 1026 of the power meter 1020 includes a scale showing anelectric power whose unit is KW. Furthermore, a zone 1028 with valuesequal to or less than a predetermined value P0 (40 KW, for example) iscolored in red indicating a power shortage as shown. The zone 1028 iscalled a red zone.

FIG. 17 is a block diagram of the electric system for driving thecombination meter 1010. As shown, the combination meter 1010 is providedwith the output limitation warning lamp 842 and its driver 880. Inaddition, a first crossed coil 1030 connected to the long hand 1022 ofthe power meter 1020, a driver 1032 for driving the first crossed coil1030, a second crossed coil 1034 connected to the short hand 1024 of thepower meter 1020, and a driver 1036 for driving the second crossed coil1034 are provided at the combination meter 1010. The drivers 880, 1032and 1036 are controlled by the power control unit 700.

F. Meter Control Processes

The following explains the software configuration of the secondpreferred embodiment. The same electric control processes as the ones ofthe first preferred embodiment are performed according to the secondpreferred embodiment. The control routine of the output limitationwarning lamp of the first preferred embodiment is not carried out inthis preferred embodiment. According to the second preferred embodiment,a control routine of the combination meter including the control ofturning on and off the output limitation warning lamp 842 is carriedout. FIG. 18 is a flow chart showing the control routine of thecombination meter. The control routine is repeatedly carried out afterevery predetermined period by the power control unit 700.

As shown in FIG. 18, the CPU of the power control unit 700 carries out aroutine for calculating a FC maximum power XQmx when idling as the firststep of this control routine (step S1100). The FC maximum power XQmxwhen idling is a parameter showing a maximum output of the fuel cell 200while idling.

FIG. 19 is a flow chart showing a routine for calculating the FC maximumpower XQmx when idling. As shown, the CPU determines whether an engineof a vehicle is idling or not by carrying out four steps from step S1110through step S1140 as the first process of this routine. At the firststep S1110, the CPU determines whether an ignition switch of thevehicle, on which the power output device for mounting on a vehicle ismounted, is on or not. At step S1120, the CPU determines whether thefuel cell 200 is operated under normal conditions or not. Thisdetermination is carried out by checking whether parameters showing astate of operating the fuel cell such as a temperature of the fuel cell200, a pressure of supplied gas of fuel, and a temperature of watercoolant are within predetermined ranges.

At step S1130, the CPU determines whether the accelerator position AP,which has been input at step S110 in the routine for setting Ed, Eb andEf (FIG. 6) called from the electric control routine, is less than apredetermined value A0 (3%, for example). At step S1140, the CPUdetermines whether the required output Ed*, which has been calculated atstep S130 in the routine for setting Ed, Eb and Ef, is less than apredetermined value (5 KW, for example).

If all the determinations at steps S1110 through S1140 are affirmative,the CPU determines that the engine is idling and proceeds to step S1150.Though the CPU determines that the engine is idling when all thedeterminations at steps S1110 through S1140 are affirmative according tothe present preferred embodiment, it is not necessary to meet all theconditions. The point is that the CPU may determine that the engine isidling when a condition under which a heavy load is not applied to thedrive motor 830 is met. For example, the determination whether theengine is idling or not may be carried out only through steps S110 andS130. The determination may also be carried out only through step S130.

At step S1150, the CPU performs the process of calculating the FCmaximum power XQmx when idling. This calculation is carried outaccording to the temperature Tf of the fuel cell 200 input at step S140of the routine for setting Ed, Eb and Ef (FIG. 6). According to thepresent preferred embodiment, a group of maps specifying avoltage-electric current characteristic at every temperature of the fuelcell 200 is stored by the ROM of the power control unit 700. Then the FCmaximum power XQmx when idling according to the temperature Tf isderived from the group of the maps. FIG. 20 shows an example of thegroup of the maps.

As shown in FIG. 20, the group of maps MPS includes pluraltwo-dimensional maps MP showing a voltage-electric currentcharacteristic, and these plural maps are provided at every temperatureTf. At step S1150, the CPU first performs the process of selecting a mapMP, which specifies the same temperature as the temperature Tf of thefuel cell 200 input at step S140, from the group of the maps MPS storedin the ROM. An Af curve showing a voltage-electric currentcharacteristic as the performance of the fuel cell 200 is recorded inany one of the maps. The CPU traces the Af curve and determines a pointPM where an output electric power, which is the product of the outputvoltage V and the output electric current I, reaches the maximum. Thenthe CPU stores the maximum electric power at the point PM as the FCmaximum power XQmx when idling in the ROM.

Then the CPU proceeds to “return” and ends the routine for calculatingthe FC maximum power XQmx when idling for the moment. If thedetermination at step S1110 is negative, in other words, the CPUdetermines that the ignition switch is not on, the CPU clears the FCmaximum power XQmx when idling previously calculated to zero (stepS1160) and proceeds to “return,” to end this routine for the moment. Onthe other hand, if any of the determinations at steps from S1120 throughS1140 is negative, the CPU immediately proceeds to “return,” to retainthe FC maximum power XQmx when idling calculated at step S1150, and endsthis routine for the moment.

When the routine for calculating the FC maximum power XQmx when idlingis ended, the CPU carries out step S1200 in FIG. 18. At step S1200, theCPU stores the sum of the FC maximum power XQmx when idling calculatedin the routine for calculating the FC maximum power XQmx when idling anda current SOC (SOCb hereafter) of the secondary battery 800 detected bythe SOC sensor 864 as the possible maximum electric power PWmx from thepower output device for mounting on a vehicle. At this time, the SOCb isderived from the value of the SOC input at step S160 in FIG. 6. In otherwords, the sum of the FC maximum power XQmx when idling, which is themaximum power of the fuel cell 200 when idling, and the current SOCb ofthe secondary battery 800, is specified as the maximum electric powerPWmx of the power output device for mounting on a vehicle.

Then the CPU carries out a calculation based on the following formula(4) and stores a result of the calculation as the currently possibleelectric power PW (current electric power) at step S1300.Current electric power PW=V×I+SOCb  (4)

The V in the formula is an output voltage of the fuel cell 200 derivedfrom a result of detection of the voltage sensor 868. The I in theformula is an output electric current of the fuel cell 200 derived froma result of detection of the electric current sensor 870. The SOCb isthe SOC of the secondary battery 800 derived from the value of the SOCinput at step S160. Then the CPU outputs control signals according tothe maximum electric power PWmx calculated at step S1200 at the firstcrossed coil 1030 to drive the long hand 1022 of the power meter 1020 sothat the long hand 1022 swings and shows the maximum electric power PWmx(step S1400). Furthermore, the CPU outputs control signals according tothe current electric power PW calculated at step S1300 at the secondcrossed coil 1034 to drive the short hand 1024 of the power meter 1020so that the short hand 1024 swings and shows the current electric powerPW (step S1500).

After carrying out step S1500, the CPU determines whether the maximumelectric power PWmx is less than the predetermined value P0 (stepS1600). As previously mentioned, the predetermined value P0 is a valueshowing the red zone provided at the scale board of the power meter1020. If the CPU determines that the PWmx is less than P0 at step S1600,the CPU turns on the output limitation warning lamp 842 (step S1700). Onthe other hand, if the CPU determines that the PWmx is equal to or morethan P0, the CPU turns off the output limitation warning lamp 842 (stepS1800). After carrying out step S1700 or S1800, the CPU proceeds to“return” to end this control routine for the moment.

G. Effects

According to the second preferred embodiment as comprised above, the FCmaximum power XQmx when idling showing the maximum electric power of thefuel cell 200 is calculated when idling. FIG. 21 is an explanatorydrawing showing a relation between the OCV and a load at the fuel cell200. As shown, when the load fluctuates according to a time t, the OCVfluctuates according to the fluctuation of the load. As the loaddecreases, the OCV increases. When the load reaches the minimum, inother words when idling, the OCV reaches the maximum. Therefore, the FCmaximum power XQmx when idling of the fuel cell 200 calculated abovebecomes a stable maximum value without an influence from the load as afactor of fluctuation.

According to the second preferred embodiment, the calculated FC maximumXQmx is stored even after idling. The sum of the XQmx and the currentSOCb of the secondary battery 800 is calculated as the maximum electricpower PWmx of the power output device for mounting on a vehicle. Whenthe maximum electric power PWmx is less than the predetermined value P0,the output limitation warning lamp 842 is turned on.

As described above, if a maximum electric power of a fuel cell isderived from a current output of the fuel cell which is being operated,a state of power shortage is frequently detected because of rapidfluctuations of the load, and then the power shortage is frequentlynotified. On the contrary, the maximum electric power of the fuel cellis a stable value, and turning on and off of the output limitationwarning lamp 842 is controlled according to the maximum electric powerPWmx calculated from the maximum electric power of the fuel cell asdescribed above according to the second preferred embodiment. As aresult, the output limitation warning lamp 842 will be turned on only ifan output of the fuel cell 200 is lowered by a failure. Therefore, anoperator can accurately be notified of the failure of the fuel cell 200without an influence of the load fluctuation. Furthermore, thenotification of the failure is carried out by the output limitationwarning lamp 842 so that the driver can immediately be notified of thefailure through the combination meter 1010 in the instrument panel.

In addition, the maximum electric power PWmx is indicated by the powermeter 1020 provided in the combination meter 1010 according to theconfiguration of the second preferred embodiment. Therefore, stableindication of the maximum electric power is possible without influencefrom the load fluctuation. Especially, the red zone 1028 showing thatthe maximum electric power PWmx is less than the predetermined value isprovided on the scale board 1026 of the combination meter 1010.Therefore, the operator can also be notified of the failure of the fuelcell 200 through the red zone 1028.

Furthermore, the short hand 1024, in addition to the long hand 1022indicating the maximum electric power PWmx, is provided at the powermeter 1020 according to the second preferred embodiment. The short hand1024 indicates the current electric power PW output from the poweroutput device for mounting on a vehicle. Therefore, a comparison betweenthe maximum electric power PWmx and the current electric power PW of thepower output device can be done easily.

According to the power output device for mounting on a vehicle of thesecond preferred embodiment, the secondary battery 800 is provided as anenergy source other than the fuel cell 200. According to a conventionalpower output device for mounting on a vehicle with two energy sources: afuel cell and a secondary battery, an output rapidly drops when thecharge of the secondary battery begins to be insufficient because of thefluctuation of the OCV of the fuel cell according to the loadfluctuation as described above. On the contrary, an operator canaccurately be notified of a failure of the fuel cell without theinfluence of the load fluctuation, as described above, even with theconfiguration including the fuel cell and the secondary batteryaccording to the second preferred embodiment.

Though the configuration in which the output limitation warning lamp 842is turned on is adopted as a notification means to notify a driver of apower shortage according to the second preferred embodiment, aconfiguration, in which a warning buzzer is rung may instead be adopted.In addition, the driver may be notified of the power shortage through asense of touch by vibration.

Though the configuration in which the output limitation warning lamp 842is provided is adopted according to the second preferred embodiment, theoutput limitation warning lamp 842 may be omitted since the driver canbe notified of the power shortage through the long hand 1022, which haslowered into the red zone of the power meter 1020. On the contrary, aconfiguration in which the power meter 1020 is omitted and the outputlimitation warning lamp 842 is provided may be adopted.

Though the configuration in which the long hand 1022 and the short hand1024 are provided at the power meter 1020 to indicate the maximumelectric power PWmx of the power output device for mounting on a vehicleand the current electric power PW respectively for comparison isadopted, a configuration in which the short hand is omitted to onlyindicate the maximum electric power PWmx may be adopted. The operatorcan be notified of the failure of the fuel cell through values pointedby the long hand 1022. Furthermore, a configuration in which indicationof the red zone 1028 is omitted may be adopted.

Though the power meter 1020 is an analog meter according to the secondpreferred embodiment, a digital meter may be adopted. For example, aconfiguration in which the maximum electric power PWmx is indicated bythe area of a zone on a display, and the indication color is changedinto red from green when the maximum electric power PWmx is less thanthe predetermined P0, may be adopted.

Though the power output device for mounting on a vehicle of the secondpreferred embodiment includes the fuel cell 200 and the secondarybattery 800 as energy sources, a configuration in which only the fuelcell 200 is provided may be adopted. With this configuration, a possiblemaximum electric power from the power output device for mounting on avehicle can be indicated on the power meter as a value calculated in theabove-described routine for calculating the FC maximum power XQmx whenidling, and the output limitation lamp can be turned on and offaccording to the value. Furthermore, the present invention can beapplied to a configuration including another energy source other thanthe fuel cell 200 and the secondary battery 800. The point is that thepresent invention can be applied to any configuration with a fuel celloutputting power as one of energy sources.

The maximum electric power PWmx and the current electric power PWaccording to the second preferred embodiment correspond to the maximumoutput and the output of the present invention respectively. Otherparameters such as the amount of hydrogen supply and the amount ofoxidizing gas may be used to calculate the maximum output and the outputas another aspect of the present invention.

Though the above-described first and second embodiments explains thepower output devices when they are mounted on the vehicle, they may bemounted on other means of transportation such as boats, ships andaircraft or other various industrial machines.

Though the preferred embodiments of the present invention have beenexplained above, the present invention, of course, is not limited tothese preferred embodiment, and various other aspects within the spiritand scope of the present invention can be embodied.

1. A power output device comprising: a fuel cell; a fuel cellcharacteristic detecting device which detects a characteristic of thefuel cell: a calculation device that calculates a parametercorresponding to a possible electric power of the fuel cell derived fromdata stored in a memory based on the characteristic detected by the cellcharacteristic detecting device; a determining device that compares thecalculated parameter with a predetermined value and for determiningwhether the possible electric power constitutes a power shortage; and anotification device that provides a notification of the power shortageto a user or driver when the determining device has determined that apower shortage exists.
 2. The power output device according to claim 1,wherein the calculation device includes a device that calculates thepossible electric power value as a maximum output under a rated voltageaccording to the detected cell characteristic.
 3. The power outputdevice according to claim 1, wherein: the fuel cell characteristicdetecting device includes a fuel cell state detecting device thatdetects a state of the fuel cell; and the calculation device includes adevice that calculates the possible electric power as an amount oflimiting output for limiting an output of the fuel cell.
 4. The poweroutput device according to claim 3, wherein the characteristic of thefuel cell detected through the fuel cell state detecting device at leastincludes a temperature of the fuel cell.
 5. The power output deviceaccording to claim 1, wherein: the fuel cell characteristic detectingdevice includes a fuel pump state detecting device that detects a stateof a fuel pump for supplying fuel gas to the fuel cell; and thecalculation device includes a device that calculates the possibleelectric power as an amount of limiting fuel gas for limiting the amountof the fuel gas supplied from the fuel pump.
 6. The power output deviceaccording to claim 5, wherein the state of the fuel pump detectedthrough the fuel pump state detecting device is a temperature of a motorfor the fuel pump.
 7. The power output device according to claim 1,wherein: the fuel cell characteristic detecting device includes acompressor state detecting device that detects a state of a compressorfor supplying pressurized oxidizing gas to the fuel cell; and thecalculation device includes a device that calculates the possibleelectric power value as an amount of limiting oxidizing gas for limitingthe amount of the oxidizing gas supplied from the compressor.
 8. Thepower output device according to claim 7, wherein the state of thecompressor detected through the compressor state detecting device is atemperature of a motor for the compressor.
 9. The power output deviceaccording to claim 1, wherein the notification device includes anotification lamp for visually carrying out the notification.
 10. Thepower output device according to claim 1, wherein the notificationdevice provides the notification of the power shortage when the state ofpower shortage is determined by the determining device while the fuelcell outputs electric power.
 11. The power output device according toclaim 9, wherein the notification device switches the notification lampfrom turning off to lighting to provide the notification of powershortage.
 12. A vehicle comprising: the power output device according toclaim 1; and a motor that generates thrust of the vehicle by electricpower from the fuel cell, wherein the notification device provides thenotification of power shortage when the state of power shortage isdetermined by the determining device while the vehicle is running by themotor.
 13. A power output device comprising: a fuel cell; a cellcharacteristic detecting device that detects a temperature of the fuelcell; a calculation device which calculates a possible electric power ofthe fuel cell based on the detected temperature; a determining devicethat determines whether the possible electric power from the fuel cellconstitutes a power shortage on the basis of the calculated possibleelectric power calculated by the calculation device; and a notificationdevice that provides a notification of the power shortage to a user ordriver when the existence of a power shortage has been determined by thedetermining device.
 14. The power output device according to claim 1,further including: an idle determining device which determines whetheran idling condition is present; wherein the calculation devicecalculates the possible electric power in response to a determinationthat the idling condition is present, such that the possible electricpower is calculated during idling; and wherein the notification deviceprovides the notification when a state of power shortage is determinedbased on the calculation of the possible electric power during theidling condition.
 15. The power output device according to claim 14,wherein the calculation device includes a plurality of maps forrespective different values of the detected characteristic at the idlingcondition.
 16. The power output device according to claim 14, whereinthe detected characteristic is a fuel cell temperature and wherein thecalculation device includes a plurality of maps for indicating possibleelectric power values for different temperatures detected during idling.17. The power output device according to claim 1, wherein thecharacteristic detected by the fuel cell characteristic detecting deviceis a fuel cell temperature, and the calculation device calculates thepossible electric power based on the detected temperature.
 18. The poweroutput device according to claim 17, wherein the detected fuel celltemperature is an idling temperature.
 19. The power output deviceaccording to claim 18, wherein the calculation device includes aplurality of maps corresponding to different idling temperatures, andwherein the plurality of maps indicate a possible power for a pluralityof idling temperatures.
 20. A power output device according to claim 19,wherein each map includes a voltage-current characteristic of the fuelcell for a corresponding idling temperature.
 21. The power output deviceaccording to claim 13, wherein the calculation device calculates thepossible electric power from a plurality of voltage-currentrelationships corresponding to a plurality of different fuel celltemperatures.
 22. The power output device according to claim 21, whereinthe plurality of relationships are provided in the form of a pluralityof maps with each map corresponding to a different temperature.
 23. Thepower output device according to claim 13, further including: an idledetermining device which determines whether an idling condition ispresent; wherein the detecting device and the calculation devicerespectively detect the temperature and calculate the possible electricpower in response to a determination that the idling condition ispresent.